Field of the Invention
The present invention relates to systems and processes for handling heavy oil residue in conjunction with combustion or other processes utilizing heavy oil residue as a feed.
Description of Related Art
Heavy oil fractions are produced at various stages in a refinery such as vacuum distillation, visbreaking, solvent deasphalting and fluid catalytic cracking. These fractions are useful as feedstocks for further refining or conversion processes and as fuel for combustion plants. Heavy oil fractions exhibit very high viscosities and levels of impurities, such as sulfur and metals. Thus conventional processes require substantial energy expenditure to make the material fluid to fit the combustion environment so that combustion efficiency is maximized, solids retention in the combustion burners is minimized, and solid particulate flue emissions is minimized. For instance, at ambient conditions, a typical vacuum residue can have a viscosity in the range of 50,000,000 centistokes, similar to some solid materials under comparable ambient conditions. Therefore, residue must be conditioned, generally by heating, to convert it into a condition suitable for pumping and injection to the combustion burners.
Heating heavy oil fractions requires energy, typically in the form of steam and/or electricity. Heating systems generally include heated storage tanks, pumps and heated transport pipes. The necessary temperature increase is accomplished with electric tracing or steam in an effort to maintain all of the heavy oil in a fluid state. Continuous motion of the heavy oil is also employed to avoid dead zones in the piping network. The entire handling system is also typically insulated to avoid cold zones that could result in increased viscosity and plugging.
Therefore, when the additional energy expenditure is subtracted from the combustion plant power output, the overall efficiency is reduced.
Accordingly, there exists a need for more efficient processes for handling heavy oil residue feedstocks by reducing the amount of external thermal energy required to maintain the material in a fluid and flowable state. There also exists a need for more efficient processes for using heavy oil residue feeds in combustion processes to increase combustion plant efficiency. There exists a further need for combustion processes with reduced CO2 emissions.